The spinal column, which is the central support to the vertebrate skeleton and a protective enclosure for the spinal cord, is a linear series of bones, or vertebrae. Intervertebral discs separate and reduce friction between adjacent vertebrae and absorb compression forces applied to the spinal column. Spinal nerves that extend from each side of the spinal cord exit the column at intervertebral forama.
A typical vertebra comprises an anterior body, and a posterior arch that surrounds the spinal cord lying within the vertebral foramen formed by the arch. The muscles that flex the spine are attached to three processes extending from the posterior arch. On the upper surface of each vertebra in a standing human are two superior articulated processes that oppose two inferior articulated processes extending from the lower surface of an adjacent vertebra. Facets on the opposing processes determine the range and direction of movement between adjacent vertebrae, and hence the flexibility of the spinal column.
Back pain is one of the most significant problems facing the workforce in the United States today. It is a leading cause of sickness-related absenteeism and is the main cause of disability for people between ages 19 and 45. Although acute back pain is common and typically treated with analgesics, chronic pain may demand surgery for effective treatment. One of the most common causes of back pain stems from trauma to an intervertebral disc, resulting from mechanical shock, stress, tumors or degenerative disease, which may impair functioning of the disc and limit spinal mobility. In many cases, the disc is permanently damaged and the preferred treatment becomes partial or total excision. Another cause of back injury is herniation of the intervertebral disc, wherein the gelatinous fluid of the nucleus pulposus enters the vertebral canal and pressures the spinal cord. Again, surgery is often the only method available for permanent relief from pain or the neurological damage ensuing from the pressure of fluid on the spinal cord, and requires replacement of the damaged disc.
Traumatic injury to an intervertebral disc that is not removed will frequently promote scar tissue formation. Scar tissue is weaker than original healthy tissue so that the disc will progressively degenerate, lose water content, stiffen and become less effective as a shock absorber. Eventually, the disc may deform, herniate, or collapse, limiting flexibility of the spinal column at that position. The only option is for the intervertebral disc to be partially or totally removed.
Surgical procedures for replacing intervertebral disc material, rather than fusing of the vertebrae, have included both anterior approaches and posterior approaches to the spinal column. The posterior approach (from the back of the patient) encounters the spinous process, superior articular process, and the inferior articular process that must be removed to allow insertion of the disc replacement material into the intervertebral space. The anterior approach to the spinal column is complicated by the internal organs that must be bypassed or circumvented to access the vertebrae.
Degenerative changes of the adult spine have traditionally been determined to be the result of the interrelationship of the intervertebral disc and the facet joints. Degenerative changes in the disc can lead to arthritic changes in the facet joint and vice versa. Although the use of an intervertebral disc prosthesis may achieve some level of success with patients, disc replacement does not address spine pathologies such as spondylolisthesis and spinal stenosis caused by facet joint degeneration or disease
It would therefore be an improvement in the art to provide an intervertebral disc prosthesis and/or a facet joint prosthesis and method that replaces the natural disc and/or facet joint so as to remove the source of arthritic, traumatic, or other disease mediated pain.